A coupling mechanism of the pre-cited type considered as generic is disclosed in US 2002/0046718 A1. The play of the piston required in the reception of the outer element for achieving coupling, causes the piston to tilt in the reception. This always occurs during cam lift because an undersurface of the piston abuts against a corresponding counter surface of the reception of the outer element. Due to the tilting of the piston, a contact zone is displaced from the interior of the reception to an edge section of this toward the parting surface between the elements. If the reception into which the piston engages is a bore, only a point contact is made. In the case of a flattened piston that is displaced, for example, into a reception in the form of an annular groove in the outer element, a two-point contact is determinable.
The aforesaid point contact in the edge section leads to an extreme augmentation of the contact forces. If, additionally, undesired large deviations of form, rectangularity and parallelism exist, the aforesaid effect is aggravated. Due to the extremely high loads acting precisely on the edge section, the play in the coupling region increases in an unfavorable manner over the operating lifetime of the cam follower. This leads to a deformation of the edge section which, in the worst case, can result in binding between the two elements.